The repair of some bone fractures requires the use of implantable bone plate and screw systems in order to hold pieces of a fractured bone together and/or promote healing of the fracture. FIG. 1 illustrates one example of a conventional bone plate 100 having a plurality of through-holes 102. As shown in FIG. 2, screws 104 can be inserted through the holes 102 in order to be threaded into the bone 106, thereby securing the bone plate 100 to a bone 106 in need of repair. In this manner, the bone plate 100 can be compressed against the bone 106 and the bone fracture can be stabilized.
Conventional bone plate and screw systems promote healing of a fracture by compressing the fracture ends together and drawing the bone fragments into close apposition with each other. Generally, bone plates can be provided with several holes and/or slots, the holes and slots either being threaded or non-threaded screw holes, depending on the type of screw being used.
Threaded screw holes (e.g., through-holes in the bone plate with internal threads) are conventionally used with specialized screws having a threaded head portion in addition to a threaded shaft. These screws are typically referred to as “locking” screws. The threaded head portion engages with the threads of the screw hole to form a locking bone plate system (e.g., the locking screw is threaded into both the bone plate and the bone). Locking screws must be inserted at a fixed, predetermined angle with respect to the bone plate, such angle being determined by the central axis of the threaded hole. Once inserted, locking screws resist loosening and ensure stability between the screw and bone plate.
Non-threaded screw holes are conventionally used with standard screws (e.g., screws with non-threaded heads). These standard screws do not lock with the bone plate and are typically referred to as “non-locking” screws. Non-locking screws can be inserted at various different angles through the bone plate screw holes, depending on the requirements of the specific application.
Disadvantages exist with both types of bone plate through-holes. For example, non-locking screws may loosen in response to micromotion of the bone reconstruction. Stable bone fixation is critical to avoid delayed healing, non-union of the fracture, and potential implant failure from screw loosening or screw breakage. Thus, non-locking screws are susceptible to these and other disadvantages.
On the other hand, locking screws are specialized screws, and much more costly than standard bone screws (with a non-threaded head). Standard bone screws can be used with threaded screw holes in order to create a locking bone plate system, however, such systems often require a bone plate height of 5 mm or greater (0.198 inches or greater) in order to provide space for accommodating the bone screw head and for enough threads to engage the bone screw shaft. Bone plates having a height of 5 mm or greater are disadvantageous because such heights may make it difficult for a surgeon to close the wound over the bone plate. For example, suturing the skin closed over a bone plate with a 5 mm height may impose extra tension on the skin and soft tissues, potentially resulting in complications such as non-healing and/or infection.
There thus remains a need for an improved bone plate and bone screw system that can provide a locking relationship while reducing or eliminating the above-described disadvantages.